Which of the following can be used in place of lime and soda ash for softening and will remove both carbonate and noncarbonate hardness?

Sodium hydroxide is an effective chemical for water softening because it increases the pH of the water, which encourages the precipitation of hardness-causing minerals. In particular, sodium hydroxide can remove both carbonate and noncarbonate hardness by converting calcium and magnesium ions into their respective hydroxides, which then precipitate out of the solution. This process effectively softens the water, making it suitable for various applications.

The capacity of sodium hydroxide to address both types of hardness makes it a versatile alternative in water treatment processes compared to lime and soda ash. Lime primarily targets carbonate hardness, while soda ash addresses both carbonate and noncarbonate hardness but is not as effective alone in treating both types as sodium hydroxide.

Understanding the role of sodium hydroxide in altering the chemical composition of the water helps in recognizing its utility in water treatment applications, particularly in contexts where a comprehensive approach to removing hardness is needed.